Suggestions:
System allows Sales return to be saved with or without invoice reference. In such cases price list number applicable, the Sales return valuation is done based on the price defined in this price list. Users can keep the Ref Inv Id (The reference invoice number against which the Sales return is taken) as blank. Price list for the valuation of goods is necessary. In the details screen item details can be entered without invoice line number reference. If no reference, some values will be taken from master and current conditions. For example, pricing is defaulted as current unless you backdate it. In current GST invoice reference number is mandatory for credit note/Sales return